Elizabeth A. Perkett

Exposure to hyperoxia decreases the expression of vascular endothelial growth factor and its receptors in adult rat lungs.

Exposure to high levels of inspired oxygen leads to respiratory failure and death in many animal models. Endothelial cell death is an early finding, before the onset of respiratory failure. Vascular endothelial growth factor (VEGF) is highly expressed in the lungs of adult animals. In the present study, adult Sprague-Dawley rats were exposed to >95% FiO2 for 24 or 48 hours. Northern blot analysis revealed a marked reduction in VEGF mRNA abundance by 24 hours, which decreased to less than 50% of control by 48 hours. In situ hybridization revealed that VEGF was highly expressed in distal airway epithelial cells in controls but disappeared in the oxygen-exposed animals. Immunohistochemistry and Western blot analyses demonstrated that VEGF protein was decreased at 48 hours. TUNEL staining demonstrated the presence of apoptotic cells coincident with the decline in VEGF. Abundance of VEGF receptor mRNAs (Flt-1 and KDR/Flk) decreased in the late time points of the study (48 hours), possibly secondary to the loss of endothelial cells. We speculate that VEGF functions as a survival factor in the normal adult rat lung, and its loss during hyperoxia contributes to the pathophysiology of oxygen-induced lung damage.

EVIDENCE FOR A LARYNGEAL CHEMOREFLEX IN SOME HUMAN PRETERM INFANTS

ABSTRACT. Studies in animals have documented the presence of a laryngeal chemoreflex. This reflex reflex in apnea when water is placed in the laryngeal area. This study of ten premature infants presents data that would support the existence of a similar reflex response in some premature infants. All ten infants studied had apnea of unknown etiology.

SEVERE BRONCHOPULMONARY DYSPLASIA: A RETROSPECTIVE REVIEW

ABSTRACT. Over a four‐year period (1974–1978), twenty‐two infants treated in the Vanderbilt Neonatal Intensive Care Unit developed bronchopulmonary dysplasia (BPD). These infants represented 2.5% of those requiring mechanical ventilation during this time (920). Thirteen of the twenty‐two had the diagnosis of clinical hyaline membrane disease (HMD). All required greater than a mean of thirty days of positive pressure ventilation and had over sixty days of oxygen exposure. Mortality in the first year, including deaths during initial hospitalization, was 36%. Follow‐up chest radiographs, developmental evaluations, physical exams, and interval histories were available in eleven of the fourteen survivors. At hospital discharge, all survivors were tachypneic and demonstrated intercostal retractions and rhonchi. Three of the eleven infants, age 2–4 years at their last visit, had a history of repeated bouts of wheezing and recurrent respiratory infections. Ten of the eleven infants had serial developmental evaluations. Of these, eight had a developmental quotient (DQ) less than 80 when first evaluated between six months and a year and their scores did not improve significantly with age.

Vascular endothelial growth factor is expressed in ovine pulmonary vascular smooth muscle cells in vitro and regulated by hypoxia and dexamethasone

Chronic lung disease in neonates results from both lung injury and inadequate repair processes. Little is known about the growth factors involved in lung injury and repair, but vascular endothelial growth factor (VEGF) has recently been reported in several animal models of lung injury. VEGF is an endothelial cell-specific mitogen, which is also known as vascular permeability factor because of its ability to induce vascular leak in some tissues. Chronic lung disease is complicated by increased vascular permeability, which can be improved by avoidance of hypoxia and in some cases by dexamethasone therapy. In many cells, hypoxia stimulates VEGF expression. Also, in some cases, dexamethasone blocks VEGF expression. This study examined the role of hypoxia and dexamethasone in regulating the expression of VEGF in pulmonary artery smooth muscle cells. An ovine VEGF cDNA fragment (453 bp) was cloned and found to be highly homologous to known human sequences for VEGF165. Sheep pulmonary artery smooth muscle cells were cultured and exposed to room air, hypoxia, and dexamethasone, alone or in combination for 6 h. At baseline these cells expressed VEGF mRNA at approximately 3.9 kb. The half-life of VEGF mRNA in the smooth muscle cells was 171 min, more than 3-fold longer than previous reports for epithelial cells. Exposure to hypoxia caused a 3-fold increase in mRNA abundance, primarily through transcriptional up-regulation. Dexamethasone blocked the hypoxia-induced increase in VEGF mRNA. The results demonstrate that hypoxia and dexamethasone are regulators of VEGF expression in ovine pulmonary artery smooth muscle cells. It is not known whether VEGF derived from these cells is involved in lung injury and/or normal homeostatsis.

Transforming growth factor-beta protein and messenger RNA expression is increased in the closing ductus arteriosus.

In full-term newborns, permanent closure of the ductus arteriosus is associated with the formation of a neointima that is characterized by extracellular matrix deposition and smooth muscle cell migration. Transforming growth factor-β (TGF-β), a potent modulator of extracellular matrix deposition and smooth muscle cell migration, has been found to play a role in the remodeling associated with several forms of vascular disease. We examined the protein and mRNA expression of the three mammalian isoforms of TGF-β(TGF-β1, TGF-β2, and TGF-β3) during ductus arteriosus closure in full-term lambs. We found that the temporal changes and cellular localization of the proteins and mRNAs of all three TGF-β isoforms were similar. TGF-β proteins and mRNAs were present in very low levels in the late-gestation fetal ductus. Within 24 h of delivery, there was enhanced expression of TGF-β in the newly forming neointima and outer muscle media; this continued to increase over the next 10 d. Increased expression of TGF-β in the inner muscle media and adventitia lagged behind that of the neointima and outer muscle media. TGF-β was not found in the luminal endothelial cells at any time. In contrast to the pattern described above, the appearance of TGF-β protein differed from that of mRNA in the vasa vasorum of the ductus wall. After delivery, there was an increase in TGF-β immunoreactivity in the smooth muscle cell layers of the vasa vasorum without any concurrent mRNA expression. The appearance of TGF-β at the time of ductus closure suggests an important role for this growth factor in the reorganization of the ductus wall after birth.

Lymphocyte and granulocyte migration across the endothelial layer of bovine pulmonary artery intimal explants towards lymphocyte conditioned medium

An intravenous infusion of endotoxin into sheep results in accumulation of equal numbers of lymphocytes and granulocytes in the pulmonary microcirculation. The role of the sequestered lymphocytes in acute lung injury is not known. The present study examines whether lymphocyte migration through pulmonary endothelium contributes to endothelial damage and also examines the effect of lymphokines on granulocyte migration. Bovine pulmonary artery intimal explants were mounted in Boyden chambers and conditioned media, prepared from bovine peripheral blood lymphocytes, was used as the chemoattractant. The rate of 51Cr labelled bovine granulocyte lymphocyte migration into intimal explants was determined over a 3 hr incubation period. Permeability changes were assessed by adding trace amounts of 14C-sucrose and 3H-water to the upper well and following their rate of equilibration with the lower well. 6-Keto-PGF1 alpha was measured in the upper well. Lymphocyte conditioned media was found to be chemotactic for both lymphocytes and granulocytes (lymphocyte migration at 60 min: lymphocyte conditioned media = 18.5 +/- 2.3%, mean +/- s.e. RPMI control = 12.5 +/- 1.5; granulocyte migration at 120 min: conditioned media = 36.1 +/- 5.7, RPMI control = 18.2 +/- 3.0). Ultrastructural examination revealed leukocyte migration followed an orderly sequence during which the leukocytes maintained close contact with the adjacent endothelial cells. No structural evidence of endothelial cell damage was seen at any time examined. Granulocyte migration was associated with an increased rate of 14C-sucrose equilibration after 2 hr of incubation (lower well counts/upper well counts at 2 hr, RPMI control = 0.18 +/- 0.02; lymphocyte conditioned medium = 0.30 +/- 0.04) indicating alteration in the endothelial barrier function. Leukocyte migration, particularly lymphocyte migration, was accompanied by a marked increase in prostacyclin accumulation (3 hr: no leukocytes, 188 +/- 17 ng/ml; lymphocytes, 560 +/- 104). These in vitro findings suggest that lymphocytes and lymphokines may be involved in acute lung injury and also that permeability changes associated with granulocyte migration may depend on the chemoattractant.

Vascular Endothelial Growth Factor (VEGF) Increases in Tracheobronchial Aspirates From Intubated Low Birthweight Infants During the First 10 Days of Life † 1721

Vascular Endothelial Growth Factor (VEGF) Increases in Tracheobronchial Aspirates From Intubated Low Birthweight Infants During the First 10 Days of Life † 1721